Merge branch 'sbus' of https://github.com/PX4/Firmware into #61-px4io-spektrum-decoder

Makefile

apps/drivers/px4io/px4io.cpp

apps/drivers/px4io/uploader.cpp

apps/px4io/dsm.c

apps/px4io/mixer.c

apps/px4io/px4io.c

apps/px4io/px4io.h

apps/px4io/sbus.c

nuttx/arch/arm/src/stm32/stm32_serial.c

nuttx/drivers/serial/serial.c

nuttx/include/nuttx/fs/ioctl.h

nuttx/include/nuttx/serial/serial.h

nuttx/include/termios.h